Abstract. The atmospheric concentration of elemental carbon (EC) in Europe during the
six-year period 2005–2010 has been simulated with the EMEP MSC-W
model. The
model bias compared to EC measurements was less than 20% for most of the
examined sites. The model results suggest that fossil fuel combustion is the
dominant source of EC in most of Europe but that there are important
contributions also from residential wood burning during the cold seasons
and, during certain episodes, also from open biomass burning (wildfires and
agricultural fires). The modelled contributions from open biomass fires to
ground level concentrations of EC were small at the sites included in the
present study, <3% of the long-term average of EC in PM10.
The modelling of this EC source is subject to many uncertainties, and it was
likely underestimated for some episodes.

EC measurements and modelled EC were also compared to optical measurements
of black carbon (BC). The relationships between EC and BC (as given by mass
absorption cross section, MAC, values) differed widely between the sites, and
the correlation between observed EC and BC is sometimes poor, making it
difficult to compare results using the two techniques and limiting the
comparability of BC measurements to model EC results.

A new bottom-up emission inventory for carbonaceous aerosol from residential
wood combustion has been applied. For some countries the new inventory has
substantially different EC emissions compared to earlier estimates. For
northern Europe the most significant changes are much lower emissions in
Norway and higher emissions in neighbouring Sweden and Finland. For Norway
and Sweden, comparisons to source-apportionment data from winter
campaigns
indicate that the new inventory may improve model-calculated EC from wood
burning.

Finally, three different model setups were tested with variable atmospheric
lifetimes of EC in order to evaluate the model sensitivity to the
assumptions regarding hygroscopicity and atmospheric ageing of EC. The
standard ageing scheme leads to a rapid transformation of the emitted
hydrophobic EC to hygroscopic particles, and generates similar results when
assuming that all EC is aged at the point of emission. Assuming hydrophobic
emissions and no ageing leads to higher EC concentrations. For the more
remote sites, the observed EC concentration was in between the modelled EC
using standard ageing and the scenario treating EC as hydrophobic. This
could indicate too-rapid EC ageing in the model in relatively clean parts of
the atmosphere.